Noble metal contacts for plating applications

ABSTRACT

Apparatus for electrochemical plating, comprising a support ring and a plurality of inwardly directed shanks extended from an inner circumference of the ring, wherein each of the shanks comprises a contacting tip brazed to the distal end the shank.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to semiconductor substrate processing systems. More specifically, the present invention relates to an apparatus for performing an electrochemical plating process in a semiconductor substrate processing system.

[0003] 2. Description of the Related Art

[0004] In ultra large scale integration integrated circuit (IC) devices (i.e., devices having more than one million logic gates), the multilevel interconnects are formed by filling the interconnect features (i.e., trenches, vias, and the like) with a metal, such as copper (Cu), aluminum (Al), and the like. Copper is the wiring material of choice in the interconnecting networks of advanced IC devices. In addition to superior electrical conductivity, copper is more resistant than aluminum (Al) to electromigration that, in operation, may destroy a thin film conductive line that carries an electrical current.

[0005] As dimensions of the interconnect features decrease and the aspect ratios increase, a void-free metal fill using conventional metallizing techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and the like, becomes increasingly difficult. As a result thereof, during manufacturing of advanced IC devices, electrochemical plating (ECP) has emerged as a production-worthy process for metallizing interconnect features.

[0006] The ECP process is, generally, a two-step process. During a first step, a seed layer (e.g., copper seed layer) is formed upon the interconnect features, as well as elsewhere on the substrate. The seed layer may extend from a device surface (i.e., plating surface) of the substrate around the beveled edges to a backside (i.e., non-plating) surface of the substrate. Generally, the seed layer is deposited using a CVD, PVD, evaporation, and the like process. Then, during a second step, the substrate is exposed to a plating solution, while an electrical bias is simultaneously applied between the substrate and an anode electrode positioned within the plating solution. The plating solution is rich in ions of the metal to be plated onto the substrate (i.e., copper) and, as such, the electrical bias causes ions of such metal to be urged out of the plating solution and deposited onto the seed layer.

[0007] The electrical bias is provided to the substrate using a plurality of electrical contacts. Typically, the same contacts are also used to provide a support to the substrate during the ECP process. Generally, such contacts are collectively bonded to a conductive support ring and engage the seed layer of the substrate. In operation, the electrical contacts apply a voltage to the seed layer, creating a current path through the plating solution. Such current path has an associated electrical resistance. The contacting surface of the tip of the electrical contact (i.e., portion of the contact having a contact with the seed layer) erodes as a result of exposure to the plating solution. Similarly, the resistance of the current path changes when a mechanical and electrical interface formed between the tip and a shank of the contact is degraded by the plating solution.

[0008] In the prior art, to extend longevity of the electrical contacts, the contacting tip may be coated with a protective layer of noble metals, such as platinum (Pt), indium (In), and the like, or with a layer of an alloy of such metals. Generally, the contacting tip is attached to a shank of the contact using fasteners, such as screws and the like. Still, the electrical contacts of the prior art have limited service life and variable contact resistance, e.g., due to the thinness of the protective coating, deterioration of the interface between the tip and shank of the contact, and the like. The changes in the contact resistance of the electrical contact result in the non-uniformity of the film plated upon the substrate and may cause the ECP process to be defective.

[0009] Therefore, there is a need in the art for an improved electrical contact that provides an electrical bias to a substrate during an electrochemical plating process.

SUMMARY OF THE INVENTION

[0010] The present invention is an apparatus for electrochemical plating, comprising a support ring having a plurality of inwardly directed shanks extended from an inner circumference of the ring, wherein each of the shanks comprises a contacting tip brazed to the distal end the shank.

[0011] In one embodiment, the contacting tip is formed from a platinum/iridium alloy and is brazed to the shank using a palladium/cobalt alloy. In another embodiment, the shanks are formed from a metal, such as niobium (Nb), tantalum (Ta), and the like, that oxidizes in a plating solution and produces a protective oxide layer upon the shank.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:

[0013]FIG. 1 is a schematic, partial perspective and sectional view of an exemplary plating apparatus according to one application of the present invention;

[0014]FIGS. 2A and 2B are, respectively, schematic, cross-sectional and top plan views of an exemplary support ring according to one embodiment of the present invention;

[0015] FIGS. 3-5 are schematic, cross-sectional views of contacts of the support ring of FIGS. 2A, 2B according to embodiments of the present invention; and

[0016] FIGS. 6A-6F illustrate an exemplary support ring at different steps of fabricating the contacts of FIG. 3 according to one embodiment of the present invention.

[0017] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.

[0018] It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

DETAILED DESCRIPTION

[0019] The present invention is an apparatus for providing an electrical bias to a substrate in a processing system performing an electrochemical plating process. The apparatus (e.g., support ring) comprises a conductive annular body supplied with a plurality of flexible current-carrying electrical contacts. The contacts are a part of or conductively bonded to the support ring. Each contact comprises a shank and a contacting tip that is brazed to the shank. In operation, the contacting tips engage a peripheral portion of the substrate. A plurality of such flexible electrical contacts may be formed using, e.g., a pre-formed ring of the platinum/iridium alloy that is brazed into the support ring and then machined to define the individual contacts.

[0020] In one embodiment, the contacting tips are formed from an alloy comprising at least two noble metals (e.g., a platinum/iridium (Pt/in) alloy and the like). In another embodiment, shanks are formed from a metal, such as niobium (Nb), tantalum (Ta), and the like, that oxidizes in a plating solution and produces a protective oxide layer upon the shank.

[0021]FIG. 1 is a schematic, partial perspective and sectional view of an exemplary electrochemical plating (ECP) apparatus 100 utilizing a support ring 150 with flexible electrical contacts 156 according to one embodiment of the present invention. FIGS. 2A and 2B are, respectively, schematic, cross-sectional and top plan views of the support ring 150. For best understanding of the invention, the reader should refer simultaneously to FIGS. 1, 2A and 2B. The images in FIGS. 1, 2A and 2B are simplified for illustrative purposes and are not depicted to scale.

[0022] The ECP apparatus 100 generally includes a head assembly 102, a substrate securing assembly 110, and a plating bath assembly 161. The head assembly 102 is attached to a base 104 using a support arm 106. In operation, the head assembly 102 defines the position and movements of the substrate securing assembly 110 that places a substrate 120 in a plating solution 165 for plating.

[0023] The plating bath assembly 161 includes an inner basin 167 that is contained within a larger outer basin 163, and an anode assembly 170. A plating solution (electrolyte) 165 is supplied to the inner basin 167 through an inlet 166 at a bottom 169 of the basin. The inlet 166 is generally connected to a supply line to a reservoir (not shown) for the plating solution 165. The outer basin 163 collects the plating solution from the inner basin 167 and drains the solution through a fluid drain 168 back to the reservoir.

[0024] The anode assembly 170 is positioned within a lower region of the inner basin 167 and provided with a diffusion plate 172 (e.g., a porous ceramic member or the like) positioned above the anode assembly 170. An electrical connection to the anode assembly 170 is provided using an anode contact 174 formed from a conductive material that is insoluble in the plating solution (e.g., platinum, platinum-coated steel, and the like).

[0025] The anode contact 174 extends through the bottom 169 and is coupled to an anode terminal of an electrical power supply (not shown), while a cathode terminal of the power supply is coupled to a support ring 150 (see discussion in reference to the substrate securing assembly 110 below). As such, the power supply provides an electrical bias between the anode assembly 170 and the substrate 120. In operation (i.e., when a substrate 120 is immersed into the plating solution), in response to the bias, an electrical ionic current (represented by current flux lines 180) flows from the anode assembly 170 to a plating surface 122 of the substrate 120. The electrical ionic current deposits the plating material onto the surface 122 and, as such, metallized the interconnecting features on the substrate 120.

[0026] The substrate securing assembly 110 comprises a mounting plate 146, a thrust plate 144, a seal plate 142, a housing 116, and a support ring 150. The substrate securing assembly 110 may also comprise an optional inflatable bladder assembly or o-ring (not shown) that applies an evenly distributed downward force to a non-plating surface 124 of a substrate 120. The mounting plate 146 and thrust plate 144 couple the substrate securing assembly 110 to the head assembly 102.

[0027] The support ring 150 comprises a plurality of flexible electrical contacts 156 that support the substrate 120. The contacts 156 are disposed around an inner circumference of the support ring 150 in a circular pattern and extend from the circumference substantially radially inward. Each contact 156 comprising a shank 301 and a contacting tip 316. Generally, the contacting tips 316 engage the substrate 120 around the edge of the substrate. In the depicted embodiment, the shank 301 extends from a midpoint 320 of the support ring 150 that is thicker than the shank. In other embodiments, the shank 301 may be coplanar with either an upper surface 322 or a bottom surface 324 of the support ring 150.

[0028] The support ring 150 is further supplied with an optional protective coating 130 to protect the contacts 156 from the plating solution 165. The protective coating 130 may comprise at least one layer of material that is chemically resistant to the plating solution, e.g., polytetrafluoroethylene-based material, such as AFLON®, TEFZEL®, KALREZ®, VITON®, and the like. Such materials are available from AG Fluoropolymers USA, Inc., Pennsylvania and other suppliers. Alternatively, the housing 116 may also be provided with such protective coating (not shown).

[0029] Generally, the housing 116 is formed from an electrically conductive material (e.g., stainless steel) coated with an insulator. As such, the housing 116 may be used to couple the support ring 150 to the power supply that facilitates the plating process. Therefore, electrical power (e.g., in a form of a controlled DC current) may be supplied to the contacts 156 by coupling the power supply either to the housing 116 or directly to the support ring 150. The contact 156 conducts an electrical current from the support ring 150 to a seed layer deposited on the substrate 120. Generally, the electrical current is supplied to the contacts 156 cooperatively. Alternatively, the current may be supplied to groups of the contacts, or to individual contacts that are electrically isolated one from another.

[0030] The support ring 150 may further comprise scallops (not shown) that are disposed along the bottom surface 324 of the ring to increase uniformity of the flux towards the plating surface 122 of the substrate 120. Such scallops are described in commonly assigned U.S. patent application Ser. No. 10/278,527, filed Oct. 22, 2002, which is incorporated herein by reference.

[0031] FIGS. 3-5 depict schematic, cross-sectional views of exemplary embodiments of contacts of the support ring 150. For best understanding of these embodiments, the reader should simultaneously refer to FIGS. 3-5. The images in FIGS. 3-5 are simplified for illustrative purposes and are not depicted to scale. Those skilled in the art will understand that the scope of the invention is not limited to such exemplary embodiments.

[0032]FIG. 3 depicts a flexible contact 350 where the contacting tip 316 is brazed into a recess 314 at the distal end of the shank 301. Accordingly, FIG. 4 depicts a flexible contact 450 where the contacting tip 316 is brazed to a sidewall 328 of the shank 301, and FIG. 5 depicts a flexible contact 550 where the contacting tip 316 is supplied with a shoulder 330 that is brazed to a sidewall 502 of the shank 301.

[0033] In depicted embodiments, the support ring 150 and the shanks 301 are formed from a single piece of material, such as a stainless steel (e.g., steel “302”) and the like. In an alternative embodiment, the stainless steel shanks 301 may be bonded to the support ring 150 using, e.g., welding, brazing, and the like. Further, the protective coating 130 is applied to protect, in operation, the contacts and support ring from the plating solution. In a further alternative embodiment, the shanks 301 may be formed from such a metal (e.g., niobium (Nb), tantalum (Ta), and the like) that will oxidize in the plating solution 165 and produce a protective oxide layer (not shown) upon the shank. When the support ring 150 comprised such oxidized shanks, the protective coating 130 is considered optional.

[0034] The shank 301 has a length and cross-sectional form factor that are selected such that the contact 156 provides support and electrical contact to the substrate 120, however, causes no damage to the surface of the substrate. In one exemplary embodiment, a length 306, thickness 308, and width 309 of the shank 301 are about 2 to 10 mm, 0.2 to 1 mm, and 0.5 to 10 mm, respectively. In this embodiment, the contacting tip 316 has a length 310 (measured on a contact surface 313), thickness 312 (measured from a surface 311 of the shank 301 to the contact surface 313), and width 315 of about 0.05 to 1 mm, 0.1 to 1 mm, and 0.5 to 10 mm, respectively. In the depicted embodiment, the width 309 of the shank 301 and the width 315 of the contacting tip 316 are the same, however, in other embodiments, the widths 309 and 315 may be different.

[0035] A number of the contacts 156 may vary, for example, according to a diameter and weight of the substrate 120. In one particular embodiment, to support a 300 mm silicon (Si) wafer, the support ring 150 and the shanks 301 were formed from a single piece of stainless steel “302”, and the support ring comprised 500 contacts 350. Each shank was 4 mm long, 0.8 mm thick, and 0.5 mm wide and comprised a contacting tip that was 0.2 mm long, 0.4 mm thick, and 0.5 mm wide.

[0036] The contacting tip 316 may be formed from an alloy that comprises at least two noble metals (e.g., platinum/indium (Pt/in) alloy having about 85% of platinum and about 15% of indium) and then bonded to the shank 301. In one embodiment, the contacting tip 316 is brazed to the shank 301 using, e.g., a palladium/cobalt (Pd/Co) alloy comprising about 65% of palladium and about 35% of cobalt.

[0037] In operation, the plating solution may cause corrosion of a contact, as well as corrosion and electrical degradation of the contacting tip and interface between the tip and shank. However, in the contacts 156, the entire contacting tip 316 is formed from a chemically resistant alloy and then brazed to the shank 301 using also a chemically resistant alloy. Brazing facilitates a high quality mechanical and electrical interface between the tip and shank. Additionally, in embodiment shown in FIG. 5, a position of a brazed interface is moved away from a contact surface 313 of the contacting tip 316 and, as such, from the plating solution. In each embodiment, the shank is covered with the protective coating 130, as discussed above. In an alternative embodiment, the shank 301 may be formed from such a metal (e.g., tantalum or niobium) that, when exposed to the plating solution, develops a protective oxide layer on the shank in lieu of using a separate protective coating 130. As such, in either embodiment, the contacts 156 provide greater longevity (service life), reliability, and performance (e.g., stability ands low value of electrical resistance) than other contacts used in the ECP apparatuses.

[0038] FIGS. 6A-6F depict a support ring at different steps of fabricating the contacts of FIG. 3 according to one embodiment of the present invention. In operation, uniform contact resistance promotes uniform plating thickness. As such, a process of fabricating the contacts intends to ensure that the contacts being formed have uniform contact resistance. The views in FIGS. 6B-6E are taken along a centerline 6-6 in FIG. 6A. For best understanding of this embodiment of the invention, the reader should simultaneously refer to FIGS. 6A-6F. The images in FIGS. 6A-6F are simplified for illustrative purposes and are not depicted to scale.

[0039]FIG. 6A depicts a top plan view of a support ring 450 before the process of fabricating the contacts begins. The support ring 450 comprises an outer region 402 and inner region 404. In the depicted embodiment, the regions 402 and 404 are formed from an annular piece of a conductive material, e.g., stainless steel “302”. The outer region 402 is thicker than the inner region 404. In one embodiment, the inner region 404 has a thickness 412 that is equal to the thickness of a contact 428 being formed, while a width 414 of the inner region 404 is generally greater than a length 411 of the contact (discussed in reference to FIG. 6E below). Generally, the inner region 404 is disposed at a midpoint 406 of the outer region 402 (discussed in reference to FIG. 6B below). Alternatively, the inner region 404 may be coplanar (not shown) with either upper (408) or bottom (410) surface of the outer region 402.

[0040]FIG. 6B depicts a portion of the support ring 450 after a groove 416 is formed in the distal portion of the inner region 404. In one embodiment, the groove 416 has a depth 418 of about 0.3 to 0.1 mm and a width 420 of about 0.5 to 10 mm. Generally, the groove 416 is adapted to receive a pre-formed ring 426 (discussed in reference to FIG. 6D below).

[0041]FIG. 6C depicts a schematic, cross-sectional view of a portion of the support ring 450 having a brazing material 422 placed and melted in the groove 416. A melting temperature of the brazing material is below melting temperatures of materials of the support ring 450 and contacting tip (discussed in reference to FIG. 6D below). When melted, the brazing material forms a layer 424 in the groove 416. In one embodiment, the brazing material comprises a palladium/cobalt alloy having about 65% of palladium and about 35% of cobalt. Such brazing material wets stainless steel “302” (inner region 404) and platinum/indium alloy (ring 426) and possesses high corrosion resistance to the plating solution, high purity, and a low vapor pressure at the brazing temperature. The palladium/cobalt alloy has a melting temperature of approximately 1220 degrees Celsius that is substantially below the melting temperature of the stainless steel “302” (approximately 1620 degrees Celsius).

[0042]FIG. 6D depicts a schematic, cross-sectional view of a portion of the support ring 450 after the pre-formed ring 426 is positioned in the groove 416 on a layer 424 of melted brazing material 472. In one embodiment, the ring 426 fits into the groove 416. The pre-formed ring 426 comprises, for example, a platinum/indium alloy having about 85% of platinum and about 15% of indium. Such alloy has a melting temperature of approximately 2230 degrees Celsius.

[0043] When heated above its melting temperature (i.e., above of approximately 1220 degrees Celsius), the platinum/indium alloy wets a bottom surface 415 of the groove 416 and a bottom surface 428 of the pre-formed ring 426. In the depicted embodiment, a width 440 of the pre-formed ring 426 is selected to fit into the groove 416 and a height 444 of the ring is selected such that a height 442 of an exposed portion of the ring is equal to that of the contacting tip 425 (discussed in reference to FIG. 6E below).

[0044] After the platinum/indium alloy is then cooled below its melting temperature, the alloy bonds the pre-formed ring 426 to the groove 426. The brazing process develops a high strength mechanical and high quality electrical interface between the pre-formed ring 426 and inner region 402. After brazing the pre-formed ring 426 into the groove 416, an extending inwardly portion of the inner region 404 (portion 430) is generally machined off to prevent, in operation, shielding of the edge of the substrate from the plating solution. Alternatively, the annular portion 430 may be removed using an EDM process (discussed in reference to FIGS. 6E and 6F below). In a further embodiment, the pre-formed ring 426 may also be machined, e.g., the edges and upper surface of the ring may be rounded or polished, and the like.

[0045]FIGS. 6E and 6F depict, respectively, schematic, cross-sectional and top plan views of a portion of the support ring 450 after a contact 428 is formed in the inner region 404. The contact 428 may be formed using, for example, an electric discharge machining (EDM) technique and the like. The EDM process removes portions 446, 448, and the like of the inner region 404 between the adjacent contacts (e.g., contacts 428 a, 428 b, and 428 c). In a further embodiment, the EDM process provides surface finishing to the contacts and/or contacting tips.

[0046] After the EDM process, the remaining portions of the inner region 404 and ring 426 form shanks 432 (e.g., shanks 432 a, 432 b, and 432 c) and contacting tips 425 (e.g., contact tips 425 a, 425 b, 425 c). The EDM process continues until all contacts 428 of the support ring 450 are fabricated as described above.

[0047] Those skilled in the art will appreciate that the contacts shown in FIGS. 4 and 5 may be fabricated using techniques that are similar to the described above in reference to the contact of FIG. 3. Similarly, to fabricate the contacts 428 having the tantalum or niobium shanks 432, the inner portion 404 of the support ring 450 may be formed from tantalum or niobium, respectively.

[0048] While foregoing is directed to the illustrative embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

What is claimed is:
 1. Apparatus for electrochemical plating, comprising: a support ring; a plurality of contacting tips disposed radially inwards of the support ring; and a plurality of shanks, each of the shanks having a first end coupled to the support ring and a second end brazed to a respective one of the contacting tips.
 2. The apparatus of claim 1, wherein the support ring and the shanks are formed from a single piece of the same material.
 3. The apparatus of claim 1, wherein the shanks are bonded to the support ring.
 4. The apparatus of claim 1, wherein the shanks are formed from stainless steel.
 5. The apparatus of claim 1, wherein the shanks are formed from a metal forming a protective oxide layer when exposed to a plating solution.
 6. The apparatus of claim 5, wherein the metal is tantalum or niobium.
 7. The apparatus of claim 1, wherein the contacting tip is brazed to a bottom of the shank.
 8. The apparatus of claim 1, wherein the contacting tip is brazed to a sidewall of the shank.
 9. The apparatus of claim 1, wherein the contacting tip further comprises: a first portion having a first end brazed to a sidewall of the shank and extending inward to a second end; and a second portion extending upward from the second end of the first portion to a contact surface adapted to support a substrate thereon.
 10. The apparatus of claim 1, wherein the support ring comprises a coating protecting the ring from a plating solution.
 11. The apparatus of claim 10, wherein the coating comprises at least one layer of a polytetrafluoroethylene-based material.
 12. The apparatus of claim 1, wherein the contacting tip is formed from a platinum/indium alloy comprising about 85% of platinum and about 15% of indium.
 13. The apparatus of claim 1, wherein the contacting tip is brazed using a palladium/cobalt alloy comprising about 65% of palladium and about 35% of cobalt.
 14. The apparatus of claim 1, wherein the contacting tip has a length of about 0.5 to 10 mm, a width of about 0.05 to 1 mm, and a thickness of at least about 0.5 mm.
 15. The apparatus of claim 1, wherein the shank of the contact has a length of about 2 to 10 mm, a width of about 0.5 to 10 mm, and a thickness of about 0.2 to 1 mm.
 16. The apparatus of claim 1, wherein the contacting tip is fabricated from at least two noble metals.
 17. Apparatus for electrochemical plating, comprising: a support ring; a plurality of electrically conductive shanks coupled to the support ring and having a distal end extending radially inward of an inner circumference of the support ring; and a plurality of electrical contact elements, each contact element having a first portion brazed to the distal end of a respective one of the plurality of shanks and a second portion extending radially inward and upward of the first end to a contact tip that is adapted to support a substrate thereon.
 18. A method of fabricating a support ring of an apparatus for electrochemical plating, comprising: providing a conductive body having an annular inner portion; forming a concentric groove in the annular inner portion; depositing a brazing material into the groove; positioning on the brazing material a ring formed from a contacting tip material; heating the brazing material to braze the ring to the annular inner portion; and machining the annular inner portion and the ring to form a plurality of contacts.
 19. The method of claim 18, wherein each contact of said plurality of contacts comprises a shank and a contacting tip.
 20. The method of claim 19, wherein the shanks are formed from stainless steel, tantalum, or niobium.
 21. The method of claim 18, wherein the ring comprises a platinum/indium alloy having about 85% of platinum and about 15% of indium.
 22. The method of claim 18, wherein the brazing material comprises palladium/cobalt alloy having about 65% of palladium and about 35% of cobalt.
 23. The method of claim 18, wherein machining removes portions of the annular inner portion and the ring between the adjacent contacts.
 24. The method of claim 18, wherein machining is electrical discharge machining. 